The invention is particularly suited for use in a magnetic inductive flowmeter (MIF), in particular in an MIF with capacitively coupled electrodes. In the case of this combination, the capacitively coupled electrodes needed for the flow measurement by means of the MIF are used simultaneously as capacitor plates for determining the level. Furthermore, the combination of the present invention with an MIF is advantageous because it is not possible to distinguish between a reduced flow rate and a reduced level of the conducting medium from the measurement signal of an MIF.
Devices for determining the level of a conducting medium in a line in connection with an MIF with galvanically coupled electrodes are known from the prior art. These are also called idling identifications, i.e., the device can tell if the line is running dry. In the case of such an idling identification, the normal flow measurement of the MIF is used at the same time to check if the line is completely filled with the conducting medium. However, the operating principle of these known idling identifications fundamentally differs from that of the invention.
The processes and devices for determining the level of a medium in a line, known from European Offenlegungsschriften 0 514 964 and 0 547 751 as well as from the republished German Offenlegungsschrift 195 31 124, constitute the starting point of the present invention. In the case of these known processes and devices, the current between two capacitor plates always is evaluated for determining the level. This leads, as is evident from the above-mentioned prior art, to a division of the capacitor plates and relatively expensive control of the capacitor plates and evaluation of the measurement signals obtained. This problem results from the fact that the current between two capacitor plates is determined essentially by the electrical properties of the medium, therefore in particular the dielectric constant .epsilon. and the electric conductivity .sigma..